Pathway of Microscope Division in Androgenesis
For pathways based on few initial divisions in the microscope have been identified as leading to in vitro androgenesis.
i) Pathway I:
The microspore divide by an equal division and two identical daughter cells contribute to the sporophyte development. Vegetative and generative cells are not distinctly formed in this pathway.
ii) Pathway II:
The division of uninucleated microspore is unequal, resulting in the formation of a vegetative and a generative cell. The Sporophytic arises throught further divisions in the vegetative cell while the generative cell either divide or does so once or twice before degenerating.
iii) Pathway III:
The uninucleate microscope undergoes a normal unequal division but pollen embryos are predominantly formed from the generative cell alone. The generative cell either does not divide at all or does so only to a limited extent.
iv) Pathway IV:
The division of microscope is asymmetrical as in pathway II. Both vegetative and generative cells divide further and contribute to the development of sporophyte.( Example: Datura innoxia, occasionally , Datura metal, Atropa belladonna).
Irrespective of the above early pattern of microspore divisions, the embryogenic pollen grains ultimately become multicellular and burst open, gradually assuming the form of a globular embryo. This is followed by the normal stages of postglobular embryogeny until the development of plant. Alternatively, the multicellular mass liberated from the bursting pollen grain proliferates to a form a callus which may later differentiate into whole plants either on same medium or on a modified medium.